Interpreting the catalytic voltammetry of an adsorbed enzyme by considering substrate mass transfer, enzyme turnover, and interfacial electron transport.

TitleInterpreting the catalytic voltammetry of an adsorbed enzyme by considering substrate mass transfer, enzyme turnover, and interfacial electron transport.
Publication TypeJournal Article
Year of Publication2006
AuthorsReda, T, Hirst, J
JournalJ Phys Chem B
Volume110
Issue3
Pagination1394-404
Date Published2006 Jan 26
ISSN1520-6106
KeywordsAdsorption, Animals, Catalysis, Cattle, Electrochemistry, Electrodes, Electron Transport, Electron Transport Complex I, Heart, Kinetics, Mitochondria, Oxidation-Reduction, Surface Properties
Abstract

Redox active enzymes can be adsorbed onto electrode surfaces to catalyze the interconversion of oxidized and reduced substrates in solution, driven by the supply or removal of electrons by the electrode. The catalytic current is directly proportional to the rate of enzyme turnover, and its dependence on the electrode potential can be exploited to define both the kinetics and thermodynamics of the enzyme's catalytic cycle. However, observed electrocatalytic voltammograms are often complex because the identity of the rate limiting step changes with the electrode potential and under different experimental conditions. Consequently, extracting mechanistic information requires that accurate models be constructed to deconvolute and analyze the observed behavior. Here, a basic model for catalysis by an adsorbed enzyme is described. It incorporates substrate mass transport, enzyme kinetics, and interfacial electron transport, and it accurately reproduces experimentally recorded voltammograms from the oxidation of NADH by subcomplex Ilambda (the hydrophilic subcomplex of NADH:ubiquinone oxidoreductase), under a range of conditions. Mass transport is imposed by a rotating disk electrode and described by the Levich equation. Interfacial electron transport is controlled by the electrode potential and characterized by a dispersion of rate constants, according to the model of Léger and co-workers. Here, the Michaelis-Menten equation is used for the enzyme kinetics, but our methodology can also be readily applied to derive and apply analogous equations relating to alternative enzyme mechanisms. Therefore, our results are highly relevant to the interpretation of electrocatalytic voltammograms for adsorbed enzymes in general.

DOI10.1021/jp054783s
Alternate JournalJ Phys Chem B
Citation Key10.1021/jp054783s
PubMed ID16471690
Grant ListMC_U105663141 / / Medical Research Council / United Kingdom